Abstract Significance: Children requiring blood and marrow transplants for malignant and nonmalignant diseases are medically fragile and highly vulnerable to significant distressful symptoms such as profound fatigue, pain, nausea, vomiting, and sleep disturbances. Patient and parent symptom management is integral to successful elimination, prevention, or treatment of symptoms. Use of meaningful real-time data would facilitate symptom management for patients and parents and facilitate better understanding of symptom characteristics and symptom clusters, the development of strategies to improve health outcomes, and the delivery of personalized care interventions when and where they are most needed. Emerging mobile health (mHealth) technologies may enable symptom management by first capturing phenotypical characteristics and biomarker data, and then providing real-time feedback directly to caregivers, patients, and providers. Additionally, these technologies may accelerate assessment and monitoring of symptoms resulting in early intervention, sustained management, and/or prevention and thus improved outcomes. However, at present, few long-term studies have been conducted to assess the integration of mobile technologies into symptom management for pediatric blood and marrow transplant (PBMT) patients. We have limited knowledge of how to support patients and caregivers use of data from mobile technologies for real-time symptom management. Moreover, we do not know exactly which strategies will be best to overcome symptom management challenges. Finally, we have limited knowledge of phenotypic characterization and biomarkers related to symptoms and symptom clusters. Purpose: This exploratory mixed methods study will examine the feasibility of using mHealth technologies to facilitate symptom management for PBMT patients and caregivers. It will also explore the feasibility of using real-time data to identify phenotypical expressions and to discover potential biomarkers in order to create interventions to better manage, eliminate, or prevent PBMT symptoms and thereby promote better health outcomes. Methods: Patients/caregivers will be asked to monitor and track relevant clinical data over 3 months using a wearable tracking device and a mobile health application (app). Data generated from the devices will be visualized as trajectories that will help us to understand symptom expressions and phenotypical characteristics. Patients and caregivers will be interviewed at baseline and months one and three of the study to discuss their challenges and successes using mobile health to monitor and manage symptoms. This study will focus on a high-risk population that may benefit substantially from the use of mobile technologies. The minimally intensive, potentially cost-effective technology used in this study will decrease the patient/caregiver burden for tracking and monitoring data.